1. Field of the Invention
The present invention relates to novel coagulant compositions comprising at least one basic aluminum polychloride or polychlorosulfate, at least one iron compound and at least one salt, and to a technique for the formulation of such novel compositions.
The present invention also relates to the use of such compositions as coagulating agents in the treatment of aqueous media and, more particularly, for water purification.
2. Description of the Prior Art
It is known to this art that the principal methods for water treatment (surface waters, effluents, wastewaters, residual water, liquid waste, and the like) essentially include a stage for the removal of suspended matter by gravity settling (sedimentation), the recovered supernatant clarified water then being subjected to a filtration stage.
To improve the conditions for sedimentation, and thus the quality of the treated water, coagulating agents have long been employed, such as, especially, iron(II), iron(III) or, alternatively, aluminum chlorides, sulfates or chlorosulfates.
Given that each of these agents is at least in part effective, certain problems remained, due mainly to increasingly strict environmental regulations regarding the quality of treated water.
Thus, iron-based compounds, essentially compounds of ferric iron, have a better capacity to render sulfides insoluble, but present the disadvantage of coloring the treated water. On the other hand, the use of aluminum-based coagulating agents does not impart a specific color to the water, but it is not possible to completely remove the sulfides therewith.
One improvement in the processes for the treatment of water employing the flocculation/settling techniques has entailed using these two types of coagulating agents in the same process. However, such methods have proved to be complex in actual practice. Indeed, in addition to multiplying the sources of coagulating agents, it is necessary to allow a specific period of time between introduction of each of said coagulating agents to permit any combined or synergistic effect by reason of the conjoint use thereof.
Moreover, solutions have also been used comprising the two coagulating agents. However, it has been observed that such mixtures were not stable and that a precipitate or a gel appeared after only a few hours, indeed a few days at most.
For this reason, the operation of pumping these mixtures, during water treatment, is complicated and the correct or proper metering of the coagulating agents in the medium is difficult to achieve or control. Consequently, in order to avoid these difficulties, it is necessary to prepare the solutions shortly prior to their use. This, of course, presents a significant disadvantage.